JP2681409B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a DC-DC converter. In particular, it relates to improvements in the flywheel circuit. More specifically,
The present invention relates to an improvement in a flywheel circuit of a DC-DC converter in which no power loss occurs and a time delay does not occur in flywheel operation.

[Conventional technology]

FIG. 4 shows a schematic configuration diagram of an example of a DC-DC converter according to the prior art.

In FIG. 4, Q is a switching means such as a p-channel enhancement type field effect transistor, L is an inductance, and C is a capacitor. The DC input voltage V _I is applied between the primary side of the switching means Q and the secondary side of the capacitor C, and the voltage V ₀ across the capacitor C is output as the DC output voltage V ₀ . R is a control circuit, which receives the DC output voltage V ₀ and the reference voltage V _R , obtains the deviation voltage ΔV, and sets the duty ratio ΔT / T so that the deviation voltage ΔV becomes zero (see FIG. 2). ) Is determined, and the switching means Q is on / off controlled so as to realize this duty ratio ΔT / T. D ₃ is a flywheel diode, and has a function of discharging the energy stored in the inductance L to the load while the switching means Q is closed, while the switching means Q is open.

In the above configuration, the flywheel diode D ₃
The DC-DC converter shown in FIG. 5 has been developed because it has a drawback that the power loss due to the forward voltage drop is not negligible.

See FIG. 5. The difference from the configuration shown in FIG. ₄ is that, instead of the flywheel diode D ₃ , a flywheel switching means Q ₄ such as an n-channel enhancement type field effect transistor is used. Then, the flywheel switching means Q ₄ are, is applied a signal generated by the control circuit R, no switching means Q and the inverse of the switching operation, the switching means for flywheel when the switching means Q is closed Q ₄ is open, and when the switching means Q is open, the flywheel switching means Q ₄ is closed to perform a flywheel operation.

[Problems to be solved by the invention]

In the improved DC-DC converter shown in FIG. 5, the problem of the forward voltage drop of the diode which is inevitable in the DC-DC converter shown in FIG. 4 is solved, but from the opening of the switching means Q to the switching means. It is not easy to smoothly execute the synchronous transition to the closed cycle of Q ₄ .
It is not impossible in terms of circuit design to realize this synchronous transfer, but there are factors such as operation delays based on the accumulated charges of the switching means Q that are difficult to grasp accurately, so even if a complicated circuit is used. However, the drawback that it is not easy to perform the synchronous transition of the two switching means completely smoothly is inevitable.

An object of the present invention is to eliminate this drawback. In a DC-DC converter in which a flywheel circuit including a switching means such as a field effect transistor is used instead of a flywheel diode, a switching means for a main circuit is used. It is an object of the present invention to provide a DC-DC converter which is improved so that the operation and the operation of the switching means for the flywheel circuit smoothly and synchronously shift.

[Means for solving the problem]

For the above-mentioned purpose, a series circuit of a switching means (Q), an inductance (L) and a capacitor (C) is connected to a DC input power source, and the voltage across the capacitor (C) is set to a DC output voltage ( V ₀ ) as a main circuit for outputting the DC output voltage (V ₀ ) and the reference voltage (V _R ) and responding to the deviation voltage (ΔV) of the switching means (Q ), A control circuit (R) for determining the duty ratio (ΔT / T) and controlling the switching means (Q) with this duty ratio (ΔT / T).
In a DC-DC converter, an inductance having a rectangular magnetization characteristic, which is connected to the primary side of the inductance (L) between the primary side of the inductance (L) and the secondary side of the capacitor (C). (SR), a diode (D ₂ ) connected to this inductance (SR), and a flywheel circuit (F) consisting of a series circuit of a parallel circuit of the _second switching means (Q ₂ ) are provided,
The flywheel circuit (F), in response to closing of said switching means (Q), when charging the second capacitor (C ₂₎ゝmonitor, said second switching means (Q ₂₎ A control electrode of the capacitor is connected to the secondary side of the capacitor (C) to open the second switching means (Q ₂ ), and in response to the opening of the switching means (Q), The charged second capacitor (C ₂ ) is connected to the second switching means (Q ₂ ) with a voltage generated instantaneously due to a change in current flowing through the inductance (SR). A flywheel circuit starting circuit (K) is provided, which is connected to the control electrode and closes the second switching means (Q ₂ ), and responds to the opening of the switching means (Q). , The flywheel circuit (F It is adapted to release the stored energy of the inductance (L) to the load DC-
Achieved by DC converter.

Further, in any of the above configurations, the flywheel circuit starting circuit (K) has a diode () connected between the primary side of the inductance (L) and the secondary side of the capacitor (C). D ₁ ) and the second capacitor (C ₂ ) connected in series, and between the primary side of the second capacitor (C ₂ ) and the secondary side of the capacitor (C). A voltage on the primary side of the inductance (L) and an inductance (SR) having the rectangular magnetizing characteristic
It is possible to use a circuit which is controlled by and whose primary side has a third switching means (Q ₃ ) connected to the control electrode of said _second switching means (Q ₂ ).

[Action]

The DC-DC converter according to the present invention constitutes a flywheel circuit F with a series circuit of a parallel circuit of a switching means Q ₂ such as a field effect transistor and a diode D ₂ and an inductance SR having a square magnetization characteristic, for example, a saturable reactor. And a series circuit of a diode (D ₁ ) connected between the primary side of the inductance (L) and the secondary side of the capacitor (C) and the second capacitor (C ₂ ), An inductance connected between the primary side of the second capacitor (C ₂ ) and the secondary side of the capacitor (C) and having a voltage on the primary side of the inductance (L) and the rectangular magnetization characteristic. is controlled by the (SR), Furaihoi its primary side and a third switching means which is connected to the control electrode of the second switching means of the (Q ₂₎ (Q ₃₎ When the switching means Q of the main circuit is closed by adding the circuit K for starting the circuit, the second switching means Q ₂ of the flywheel circuit should be kept open during the period. When the switching means Q of the main circuit is opened by charging the capacitor C ₂ of the main circuit, the inductance SR having the rectangular magnetizing characteristic, for example, the voltage instantaneously generated in response to the change of the current flowing into the saturable reactor is used. Then, the above-mentioned charged second capacitor C ₂ is connected to the _second switching means Q ₂ , and this is closed, the flywheel circuit F is operated, and the switching means Q of the main circuit is closed again. Then, the second switching means Q ₂ is opened to end the operation of the flywheel circuit F.

〔Example〕

Hereinafter, with reference to the drawings, according to two embodiments of the present invention
The DC-DC converter will be described.

First Example FIG. 1 is a schematic block diagram of a DC-DC converter according to a first example of the present invention.

In the figure, Q is a switching means such as a p-channel enhancement type field effect transistor, L is an inductance, and C is a capacitor. The DC input voltage V _I is applied between the primary side of the switching means Q and the secondary side of the capacitor C, and the voltage V ₀ across the capacitor C is output as the DC output voltage V ₀ . R is a control circuit, which inputs a DC output voltage V ₀ and a reference voltage V _R to obtain a deviation voltage ΔV, and a duty ratio ΔT / T (see FIG. 2) that makes the deviation voltage ΔV zero. ) Is determined, and the switching means Q is on / off controlled so as to realize this duty ratio ΔT / T. A flywheel composed of a series circuit of an inductance SR having a square magnetizing characteristic connected to the primary side of the inductance L, a diode D ₂ connected to the inductance SR, and a parallel circuit of a _second switching means Q _2. A circuit F, a series circuit of a diode D ₁ connected between the primary side of the inductance L and a secondary side of the capacitor C, and the second capacitor C _2, and the second capacitor C ₂
Connected between the primary side of the capacitor C and the secondary side of the capacitor C and controlled by the voltage of the primary side of the inductance L and the inductance SR having the rectangular magnetizing characteristic, the primary side of which is controlled by the second side. a flywheel circuit activate circuit K and a third switching means Q _3, which is connected to the control electrode of the switching means Q ₂ is a component according to the gist of the present invention.

Refer to FIG. 2. Hereinafter, referring to the time chart shown in FIG.
The first embodiment of the present invention is shown in the schematic block diagram of FIG.
The operation of the DC-DC converter will be described.

When the switching means Q (p-channel enhancement type field effect transistor in this example) of the main circuit is closed, the DC input voltage V _I is applied to the capacitor C and the load through the inductance L, and when the capacitor C is charged, Then, the DC output voltage V ₀ is applied to the load. Since the DC output voltage V ₀ is also applied to the control circuit R, it is compared with the reference voltage V _R here, and the duty ratio ΔT / T is determined according to the deviation voltage ΔV, and the switching of the main circuit is performed. The means Q is controlled so as to be closed during the ΔT period and open during the (T−ΔT) period, and the DC output voltage V ₀ matching the reference voltage V _R is supplied to the load.

While the switching means Q of the main circuit is closed, a positive voltage is applied to the base of the npn transistor Q _{3 to} close it, so that the second switching means Q ₂ (which constitutes the flywheel circuit F ₂ In this example, the n-channel enhancement-type field effect transistor) is open circuit, and no current flows through the flywheel circuit F. However, during this period, the second capacitor C ₂ is charged.

Next, the control circuit R operates after the period of ΔT has elapsed,
When the switching means Q of the main circuit is opened, the electric charge stored in the capacitor C and the energy magnetically stored in the inductance L are released, and the DC output is continuously supplied.

At this time, since the potential of the primary side of the inductance L ((shown by A in the figure) decreases, the current flows through the diode D ₂ and the inductance SR (saturable reactor in this example) having the rectangular magnetization characteristic). Although the current begins to flow, the inductance SR having the rectangular magnetization characteristic momentarily functions as a large inductance and generates a reverse voltage, so that the potential at the point A momentarily becomes a negative potential.
The n-transistor Q ₃ is open and the second, already charged,
The positive potential of the capacitor C ₂ of the second switching means Q ₂ is applied to the gate of the second switching means Q ₂ , the second switching means Q ₂ is closed, the flywheel circuit F becomes conductive, and it is stored in the inductance L. Energy is released through this flywheel circuit F. Then, this state is maintained until the npn transistor Q ₃ is closed.

On the other hand, the inductance SR having the rectangular magnetizing characteristic saturates with a slight current inflow and does not function as an inductance thereafter, so that a large amount of power loss does not occur in the flywheel circuit F.

The flywheel circuit F is maintained in the conductive state through the diode D ₂ even if the second switching means Q ₂ is opened during the period when the switching means Q is open. Therefore, it is highly reliable.

In addition, the resistors R ₁ , R _2, and R ₃ are all current control resistors and have no significant meaning to the circuit operation. On the other hand, the diode D ₄ is just a protection measure, which again does not significantly affect the circuit operation.

When the period T has been completed and the switching means Q is closed again, the initial state is restored, but at this time, the second switching means Q ₂ is still closed. However, since the inductance SR having the square magnetizing characteristic exhibits a large inductance value when the direction of the current flow is reversed, a voltage is generated across the inductance SR having the square magnetizing characteristic and the potential at the point A rises. . And at that time
npn base to the positive voltage of the transistor Q ₃ is applied, npn transistor Q ₃ is by closed, so that the second switching means Q ₂ is opened. Therefore, there is a slight time delay until the npn transistor Q ₃ is closed and the second switching means Q ₂ is opened.
The second switching means Q _2, since only a flow limited small current by the large inductance value of the inductance SR having rectangular magnetization characteristics, in reality, it does not involve any disadvantage.

As described above, the DC-DC converter having the circuit configuration shown in FIG. 1 automatically follows the open / close path of the switching means Q, and the flywheel circuit F shifts between the non-conducting state and the conducting state. However, the flywheel circuit F is not accompanied by forward loss, and the flywheel operation can be performed by quickly following the opening and closing of the switching means Q.

Second Example See FIG. 3 The difference between this example and the first example is that the gate potential of the _second switching means Q ₂ constituting the flywheel circuit F is negative while the switching means Q is closed during the closed period. The second switching means Q ₂ is kept open and the second switching means Q ₂ is opened, and the potential of the second capacitor C ₂ is opened during the opening of the switching means Q to form the flywheel circuit F. The n-channel enhancement type field effect transistor is used as the switching means Q ₃ which is given to the gate of the switching means Q ₂ of the above and closed. It is only related to some minor changes. Yes, the basic operation is exactly the same.

〔The invention's effect〕

As described above, in the DC-DC converter according to the present invention, the series circuit of the switching means, the inductance and the capacitor is connected to the DC input power source, and the voltage across the capacitor is output as the DC output voltage. It has a main circuit, receives the DC output voltage and the reference voltage, determines the duty ratio of the switching means in response to the deviation voltage, and controls the switching means with this duty ratio. Has a control circuit
In the DC-DC converter, between the primary side of the inductance and the secondary side of the capacitor, an inductance having a square magnetizing characteristic connected to the primary side of the inductance, for example, a saturable reactor and this inductance, for example, A flywheel circuit including a series circuit of a diode connected to the saturation reactor and a parallel circuit of the second switching means is provided, and the flywheel circuit responds to the closed circuit of the switching means, When the second capacitor is charged, the second switching means is opened, and, in response to the opening of the switching means, the current flowing through the inductance having the rectangular magnetizing characteristic, for example, the saturable reactor. With the voltage generated instantaneously due to the change of
A flywheel circuit activation circuit is provided for closing the second switching means using the charged second capacitor, the flywheel circuit starting circuit being responsive to opening of the switching means. Since the flywheel circuit of the present invention discharges the stored energy of the inductance to the load, the problem of the forward voltage drop of the flywheel diode is solved, and further, the main circuit The operation of the switching means for the flywheel circuit and the operation of the switching means for the flywheel circuit are improved so as to smoothly and synchronously shift.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a DC-DC converter according to the first embodiment of the present invention. FIG. 2 is a time chart for explaining the operation of the DC-DC converter according to the first embodiment of the present invention. FIG. 3 is a schematic block diagram of a DC-DC converter according to the second embodiment of the present invention. FIG. 4 is a schematic block diagram of a conventional DC-DC converter. FIG. 5 is a schematic block diagram of an improved DC-DC converter according to the prior art. Q ...... main circuit switching means, L ...... main circuit inductance, C ...... main circuit capacitor, V ₁ DC input voltage ...... main circuit, V ₀ the DC output voltage of the ...... main circuit, R ...... Constant voltage controller for main circuit, V _R ...... Main circuit reference voltage, ΔV …… Main circuit deviation voltage, T …… Main circuit chopper control cycle, ΔT …… Main circuit conduction period, F …… Fly wheel circuit, SR ...... inductance having a square magnetization characteristic of the flywheel circuit (saturable reactor), a second switching means Q ₂ ...... flywheel circuit, D ₂ ...... flywheel circuit of a diode, K ...... fly Wheel circuit start-up circuit, C ₂ …… Flywheel circuit start-up circuit second capacitor, D ₁ …… Flywheel circuit start-up circuit diode, Q ₃ …… Flywheel circuit start-up circuit Third switching means, R ₁ , R ₂ , R ₃ ... current limiting resistance of flywheel circuit starting circuit, D ₄ ... protection diode of flywheel circuit starting circuit, A ... main circuit inductance A point on the primary side of L, D ₃ ... flywheel diode of DC-DC converter according to related art, Q ₄ ... n-channel enhancement type field effect transistor for flywheel circuit of DC-DC converter according to related art.

Claims (3)

(57) [Claims] 1. A series circuit of a switching means (Q), an inductance (L) and a capacitor (C) is connected to a DC input power source, and the voltage across the capacitor (C) is a DC output voltage (V ₀ ) as the main circuit
The DC output voltage (V ₀ ) and the reference voltage (V _R ) are input, and the duty ratio (ΔT / T) of the switching means (Q) is determined in response to the deviation voltage (ΔV) thereof. In a DC-DC converter having a control circuit (R) for controlling the switching means (Q) with a duty ratio (ΔT / T), a primary side of the inductance (L) and a secondary side of the capacitor (C) are provided. In between, the inductance (L)
From a series circuit of a parallel circuit of an inductance (SR) having a square magnetizing characteristic connected to the primary side of the diode, a diode (D ₂ ) connected to the inductance (SR) and a second switching means (Q ₂ ). A flywheel circuit (F) is provided, and the flywheel circuit (F) charges the _second capacitor (C ₂ ) in response to the closed circuit of the switching means (Q). Second switching means (Q ₂ )
Is connected to the secondary side of the capacitor (C) to open the second switching means (Q ₂ ), and in response to the opening of the switching means (Q), the inductance ( The charged second capacitor (C ₂ ) is connected to the control electrode of the _second switching means (Q ₂ ) with a voltage generated instantaneously due to the change of the current flowing in SR). A flywheel circuit starting circuit (K) for closing the _second switching means (Q ₂ ) is provided, and the flywheel circuit (F) is responsive to the opening of the switching means (Q). Is the inductance (L)
DC, which releases the stored energy of
-DC converter. 2. The DC-DC converter according to claim 1, wherein the inductance (SR) having the rectangular magnetizing characteristic is a saturable reactor. 3. A circuit (K) for starting the flywheel circuit.
Is a diode (D ₁ ) connected between the primary side of the inductance (L) and the secondary side of the capacitor (C).
And said second capacitor (C ₂₎ a series circuit of a, the second capacitor (C ₂₎ of the primary side to the capacitor (C)
Connected to the secondary side of the inductor (L) and controlled by the voltage on the primary side of the inductance (L) and the inductance (SR) having the rectangular magnetizing characteristic, the primary side of which is the second switching means (Q ₂ ). The DC-DC converter according to claim 1 or 2, further comprising a _third switching means (Q ₃ ) connected to the control electrode of.